Ryosuke Asatoab,
Colin J. Martinb,
Yohan Gisbertc,
Seifallah Abidc,
Tsuyoshi Kawaiab,
Claire Kammererc and
Gwénaël Rapenne*abc
aDivision of Materials Science, Nara Institute of Science and Technology, NAIST, 8916-5 Takayama-cho, Ikoma, Nara 630-0192, Japan. E-mail: gwenael-rapenne@ms.naist.jp
bInternational Collaborative Laboratory for Supraphotoactive Systems, NAIST-CEMES, CNRS UPR 8011, 29 rue Marvig, F-31055 Toulouse Cedex 4, France
cCEMES, Université de Toulouse, CNRS, 29 rue Marvig, F-31055 Toulouse Cedex 4, France
First published on 7th June 2021
The synthesis of ruthenium complexes incorporating an overcrowded pentaarylcyclopentadienyl ligand has been investigated, and higher efficiency has been reached using chlorine-functionalised precursors when compared with their brominated counterparts. A new methodology for the preparation of chlorocyclopentadienes has been developed which is well adapted for highly sterically hindered compounds and works with either electron rich or poor systems.
Coordination chemistry is a very versatile and efficient way to assemble mechanical subunits, allowing for the production of a large and diverse range of molecular machines. Many ligands are available and a vast number of metal centres can be chosen to vary and complexify molecular architectures.2 In this field the pentaphenylcyclopentadienyl anion is a common and useful ligand, with functionalised analogues already applied as rotors in various molecular machines3 including molecular motors4 and gears.5 Interest in this ligand started as a result of the availability of pentaphenylcyclopentadiene precursors which can be readily synthesised in large quantities and are air stable. Such hindered ligands are also more electron-withdrawing than their cyclopentadienyl and pentamethylcyclopentadienyl anionic analogues and their large volume is reported to confer enhanced kinetic stability towards organometallic derivatives.6 Interestingly, the reactivity pathways of pentaarylcyclopenta-dienyl ligands (Cp5Ar) seems to vary significantly when compared to cyclopentadiene (Cp) and pentamethylcyclopentadiene, due to both differences in the steric hindrance at the Cp ring and the electronic contributions from the metal-Cp coordination. These propeller shaped ligands are capable of conferring novel steric and electronic properties to metal centres7 and can also be deposited on metal surfaces chirally, with both left- and right-handed propeller chirality being represented and recognised.4c In such case, a pentaphenylcyclopentadienyl ligand functionalised with bromine atoms in the five para positions is exploited both as an anchoring subunit and as a chiral surface, contributing to the unidirectionality in the movement of the upper rotating units. Unique properties also arise from a combination of electronic effects and the steric hindrance provided by the five phenyl substituents, including protection of the metallic centre and influence on the electron releasing ability of the complex. It has also been shown that coordination of the peripheral phenyl rings can occur in place of the central cyclopentadienyl one,8 giving rise to highly dissymmetric compounds.
Among the available metals, ruthenium offers a very interesting target for preparing stable and inert heteroleptic complexes, however the coordination of ruthenium to highly sterically constrained ligands is not an easy task. Many previous attempts to directly coordinate pentaarylcyclopentadienyl (Cp5Ar) ligands from RuCl3 (ref. 9) or [Ru(p-cymene)Cl2]2 (ref. 10) failed, mainly due to the steric hindrance of the phenyl groups on the Cp ligand. As an alternative, the triruthenium dodecacarbonyl cluster Ru3(CO)12 is recognised as a reliable source of ruthenium(0) for the preparation of halogenodicarbonyl(η5-1,2,3,4,5-pentaaryl)cyclopentadienyl ruthenium(II) complexes Cp5ArRu(CO)2X. Indeed, in 1989 Manners reported the synthesis of Cp5PhRu(CO)2Br starting from Ru3(CO)12 and 5-bromo-1,2,3,4,5-pentaphenylcyclopenta-1,3-diene in refluxing toluene (Scheme 1, left).11 This reaction proceeds via the formal oxidative addition of the brominated cyclopentadiene precursor onto ruthenium(0) and involves a transient cyclopentadienyl radical intermediate. In the last decades, the scope of this reaction has been expanded to include a variety of para-substituted pentaphenylcyclopentadienes, as precursors of ruthenium-based molecular machines.12 In addition, the analogous chlororuthenium complex Cp5PhRu(CO)2Cl has been successfully prepared from the corresponding chlorocyclopentadiene and exploited as a catalyst for the dynamic kinetic resolution of secondary alcohols.13 To avoid preparation of potentially unstable halogenocyclopentadienes, new conditions for the synthesis of this family of complexes were developed by Martin-Matute et al., involving the direct oxidative addition of bare pentaphenylcyclopentadiene Cp5PhH onto Ru3(CO)12.14a However this reaction only proceeds under very harsh conditions (160 °C for several days in a decane/toluene mixture) giving the corresponding ruthenium hydride intermediate, which finally yields Cp5PhRu(CO)2X (X = I, Br, Cl) after treatment with the appropriate haloform (Scheme 1, right). Even though some variations in aryl groups have been achieved,14 the relatively high temperatures required has limited the use of this process when cyclopentadienyl ligands bearing sensitive substituents are involved.
Scheme 1 Coordination of ruthenium to the pentaphenylcyclopentadiene ligand by previously published procedures.11,14 |
In our efforts towards the development of photo-controlled molecular machines, we aimed to introduce a terarylene photochrome on the cyclopentadienyl rotating subunit of a ruthenium complex.15 Given the synthetic cost and sensitivity of the terarylene moiety, the direct oxidative addition of the cyclopentadiene precursor Cp5ArH was ruled out and we instead turned our attention to Manners' method, starting from the bromocyclopentadiene carrying four phenyl groups and a terarylene fragment (Scheme 2). Strikingly, its reaction with Ru3(CO)12 was inoperative due to decomposition of the bromine precursor via radical side-reactions, preventing formation of the desired ruthenium complex. To understand the influence of the substituents located on the cyclopentadiene ring on this complexation reaction, we decided to investigate the reactivity of a series of brominated tetraphenylcyclopentadienes bearing one aryl group with particular electronic and/or steric properties. As an alternative, the chlorinated analogues were also prepared and their reactivity studied.
Scheme 2 Photochrome-functionalised tetraphenylcyclopentadiene brominated precursor unable to coordinate to ruthenium via reaction with Ru3(CO)12. |
Here we report the preparation of a series of ruthenium pentaarylcyclopentadienyl complexes via halogen containing intermediates, in good to excellent yields even with very crowded Cp ligands such as mesityl or terarylenyl substituents.
The same reaction conditions applied to the two sterically-hindered Cp ring containing molecules CpOHAr3 and CpOHAr4 were also found to be ineffective. We noticed that using HBr in acetic acid, led to the decomposition of the compounds with no starting material detected. This may be due to the instability of the brominated Cp's generated and/or because an electron accepting group destabilises the cation, not allowing for the elimination of the oxonium ion generated under acidic conditions.
To overcome this lack of reactivity towards acidic bromination, J.-Y. Thépot and Lapinte reported the conversion of cyclopentadienol derivatives to their brominated analogues using a SOBr2–pyridine mixture instead of HBr in acetic acid.7d Since the mechanism of halogenation is different in the case of SOX2 compared to HX (X = Cl or Br), different results could be expected, especially as the sulfur-containing by-products further decompose to volatile SO2 gas rendering the process irreversible (Scheme 5). As shown on Scheme 4, the SOBr2–pyridine reagents allowed the conversion of the electron deficient cyclopentadienol CpOHAr2 to its bromo derivative in 82% yield and the sterically-hindered bromocyclopentadiene carrying a mesityl substituent CpBrAr3 was prepared in 44% yield. Interestingly for the attempted reaction of CpOHAr4 with thionyl bromide, the desired CpBrAr4 product was obtained as an inseparable mixture with its chlorinated counterpart CpClAr4 and the hydrogenated analogue CpHAr4. This side-reactivity likely results from the washing of the reaction mixture during workup with dilute aqueous HCl,7d and highlights the increased stability of the chlorinated cyclopentadiene CpClAr4 as compared to its brominated analogue.
In the case of SOX2 with or without pyridine, the envisioned mechanisms will be a competitive mixture of SN1, SNi, SN2 and SN2′ processes depending on the substrate, the solvent and the presence of pyridine (Scheme 5). As with the HBr reaction, the SN1 mechanism gives a mixture of three regioisomers (in red) while the SNi pathway (in blue) gives only one and the SN2 gives one direct compound (in black) along with two others via a SN2′ variation (in green). In consequence a 66:30:4 ratio of regioisomers was obtained for CpBrAr2, as determined by integrating the three sets of pyrimidyl protons signals on the 1H NMR spectrum (Fig. S3†). In the case of the mesityl-containing CpBrAr3, only one regioisomer has been obtained with or without pyridine, in agreement with the results obtained by Thépot and Lapinte.7d In this case, the bromine atom is located at the 3-position of the Cp ring related to the mesityl moiety, i.e. on the less sterically hindered position. This indicates that the SN1 mechanism might not be followed for this substrate.
Given the higher stability of chloro- vs. bromocyclopentadiene observed with CpBrAr4, we next explored the possibility of selectively forming the chlorinated derivatives of the sterically-hindered cyclopentadienol rings using a SOCl2–pyridine system in diethyl ether.19 The reaction proceeded smoothly with the chloride derivative of the terarylene (CpClAr4) obtained with a yield of 74%. The pyridine is generally used with thionyl chloride or bromide for the halogenation of secondary alcohols via a SN2-type mechanism, whereas if pyridine is not used, an intramolecular SNi mechanism can also take place. In the case of the sterically constrained precursors, the SN2 mechanism is kinetically difficult because of the low access available to the carbon atom. This is the reason why we next tested the reaction without pyridine. Reaction of the cyclopentadienol derivatives with SOCl2 in benzene proceeded well in all cases, presumably via a SN1 or SNi nucleophilic substitution mechanisms,20 with yields from 61% for the highly sterically constrained mesityl derivative (CpClAr3) to 87, 91 and 96% for compounds CpClAr4,15 CpClAr1 and CpClAr2 respectively. This method is very well adapted for highly sterically hindered compounds and is working very well for both electron rich and poor systems.
CpClAr1 was obtained as a mixture of three regioisomers with the chlorine atom at three possible positions of the Cp ring due to the SN1 mechanism (Scheme 5, red products). Their respective proportion can be quantified by 1H-NMR, using the equivalent methyl groups of the tert-butyl substituent as a probe. Three singlets were obtained (Fig. S5†), corresponding to the three regioisomers, with a 46:34:20 ratio which slightly differs from the statistical mixture of 40:40:20 expected from a SN1 mechanism, due to the varying stabilities of the carbocations involved as a result of the presence of the tert-butylphenyl donor substituent. A 57:37:6 ratio of regioisomers has been obtained for CpClAr2 (Fig. S7†). In the case of CpClAr4, it has not been possible to determine a ratio as the methyl signals are usually very broad in such terarylene fragments and no other region of the spectrum could be exploited for this purpose. However, the presence of these mixtures of regioisomers is not an issue as in the next step the aromatisation of the Cp ring through η5-coordination to the ruthenium centre leads to the same single cyclopentadienide complex in all cases.
In the case of the sterically crowded, electron donating, mesityl substituent CpClAr3 (Fig. S9†) one single regioisomer is obtained as for the brominated analogue. The 1H NMR spectrum also shows that rotation of the mesityl moiety is blocked, as evidenced by the non-equivalence of the aromatic and methyl protons located on this bulky group.
In the case of precursors CpXAr1, the reaction yields are similar whichever halogen derivative is present (63 and 74% for Br and Cl respectively) but surprisingly for the sterically overcrowded Cp systems the chlorinated precursors gave significantly improved yields over the brominated ones, with 59% obtained in the case of the mesityl-functionalised tetraphenylcyclopentadiene CpClAr3 compared to 14% for CpBrAr3. In the case of the electron poor terarylene-functionalised cyclopentadienyl ligand, the ruthenium complex has been obtained with a yield of 56% (ref. 15) from the chlorinated precursor CpClAr4, while it is inaccessible using its brominated analogue. Despite both the changes in halogen atom present and the varying steric effects of the Ar groups the electronic character of these complexes remains largely the same as reflected in the similar CO stretches in their IR spectra. It appears that the use of a chloride instead of a bromide offers a new pathway for the preparation of novel cyclopentadienylruthenium complexes in cases where the steric hindrance around the Cp ligand is large. The use of chlorine-functionalised pentaarylcyclopentadienyl precursors, similar to those developed here opens up a new synthetic route for the preparation of molecular motors containing sterically hindered pentaarylcyclopentadienyl ligands.
As a representative example of this pathway, exploiting this new synthetic methodology we recently reported the use of these chlorinated derivatives in the preparation of a photochromic molecular motor containing the terarylene unit Ar4. This was achieved using CpClAr4 and Ru3(CO)12 in conjunction with our previously reported tris[(ethylsulfanyl)methyl]indazolylborate surface anchor to give a new ruthenium based molecular motor.15
Rf = 0.4 (SiO2, ethyl acetate/hexane 3:7); mp 233 °C; 1H NMR (300 MHz, (CD3)2SO, 25 °C): δ 8.98 (s, 1H, Ha), 8.81 (s, 2H, Hb), 7.22–7.14 (m, 6H, HPh), 7.12–6.95 (m, 14H, HPh), 6.87 (s, 1H, OH); 13C{1H} NMR (75 MHz, CD2Cl2, 25 °C): δ 168.4 (Ca), 168.4 (Cb), 161.3 (Cquat), 157.0 (Cquat), 149.3 (Cquat), 149.2 (Cquat), 148.0 (Cquat), 143.8 (CPh–H), 143.3 (CPh–H), 142.4 (CPh–H), 142.1 (CPh–H), 141.7 (CPh–H), 141.4 (CPh–H), 101.5 (Cquat–OH); HR-MS (DCI-CH4): calcd for C34H24N2O [MH]+: 465.1940, found 465.1960; and calcd for C33H23N2O [M]+: 464.1889, found 464.1881.
2,3,4,5-Tetraphenyl-1-(pyrimidin-5′-yl)cyclopenta-2,4-dien-1-ol CpOHAr2 (200 mg, 0.43 mmol, 1 eq.) was placed in a Schlenk tube containing a magnetic stir bar and anhydrous diethyl ether (10 mL) and freshly distilled pyridine (44 μL, 0.54 mmol, 1.25 eq.) were added. The mixture was cooled down to −10 °C and thionyl bromide (42 μL, 0.54 mmol, 1.25 eq.) was added. The medium was then allowed to warm up to room temperature over one hour, under stirring. It was then neutralised by adding it slowly to 20 mL of a 1 M aqueous hydrochloric acid solution. The product was extracted with ethyl acetate (150 mL) and washed three times with water (3 × 150 mL). The organic layer was dried over magnesium sulfate and the solvents were removed by rotary evaporation. The crude product was purified by column chromatography (SiO2, ethyl acetate/cyclohexane 1:9) to afford the desired brominated product. Nevertheless, traces of impurities were still observed in some batches, so the product was further recrystallised from boiling heptane and rinsed with ice-cold pentane to give CpBrAr2 in 82% yield (187 mg, 0.36 mmol) as a yellow solid composed of a 66:30:4 mixture of regioisomers.
Rf = 0.41 (SiO2, ethyl acetate/hexane 3:7); elemental analysis: found: C, 75.0; H, 4.18; N, 5.26. Calc. for C33H23BrN2: C, 75.14; H, 4.40; N, 5.31; 1H NMR (300 MHz, CD2Cl2, 25 °C, 66:30:4 mixture of regioisomers): δ 9.05 (s, 0.04H, Haregio3), 8.91 (s, 0.30H, Haregio2), 8.86 (s, 0.66H, Haregio1), 8.78 (s, 0.08H, Hbregio3), 8.27 (s, 1.32H, Hbregio1), 8.24 (s, 0.60H, Hbregio2), 7.55–7.46 (m, 2H, HPh), 7.36–6.84 (m, 18H, HPh); 13C{1H} NMR (75 MHz, CD2Cl2, 25 °C, 66:30:4 mixture of regioisomers): δ 157.6 (Cpyr–H), 157.3 (Cpyr–H), 157.2 (Cpyr–H), 156.4 (Cpyr–H), 150.2 (Cquat), 145.5 (Cquat), 142.4 (Cquat), 142.2 (Cquat), 134.9 (Cquat), 134.8 (Cquat), 134.5 (Cquat), 134.4 (Cquat), 134.0 (Cquat), 133.9 (Cquat), 133.5 (Cquat), 131.1 (CPh–H), 130.9 (CPh–H), 130.7 (CPh–H), 130.6 (CPh–H), 130.3 (CPh–H), 130.1 (CPh–H), 129.3 (CPh–H), 129.0 (CPh–H), 128.9 (CPh–H), 128.7 (CPh–H), 128.5 (CPh–H), 128.4 (CPh–H), 128.3 (CPh–H), 128.1 (CPh–H), 128.0 (CPh–H), 127.9 (CPh–H), 127.7 (CPh–H), 75.9 (Cquat–Br); HR-MS (ESI+): calcd for C33H24BrN2 [MH]+: 529.1108, found 529.1114.
Rf = 0.8 (SiO2, dichloromethane/hexane 1:4); MS (DCI-NH3) of the mixture of products: m/z 826 (CpBrAr4, [M + H]+, 9%), 780 (CpClAr4, [M + H]+, 100), 746 (CpHAr4, [M + H]+, 52).
1-(4-(tert-Butyl)phenyl)-2,3,4,5-tetraphenylcyclopenta-2,4-dien-1-ol CpOHAr1 (100 mg, 0.19 mmol, 1 eq.) was placed in a Schlenk tube containing a magnetic stir bar. Benzene (2 mL) and thionyl chloride (84 μL, 1.16 mmol, 6 eq.) were added and the suspension was refluxed using a preheated oil bath for 30 minutes. The reaction medium was then cooled down, diluted with diethyl ether (20 mL) and washed with a saturated aqueous solution of sodium hydrogen carbonate (20 mL) followed by distilled water (2 × 20 mL). The organic layer was dried with magnesium sulfate and the solvent was then removed using rotary evaporation. The crude product was purified by column chromatography (SiO2, dichloromethane/hexane 1:1) to give pure product CpClAr1 in 91% yield (94 mg, 0.18 mmol) as a pale-orange solid composed of a 46:34:20 mixture of regioisomers.
Rf = 0.8 (SiO2, dichloromethane/hexane 1:1); 1H NMR (300 MHz, CD2Cl2, 25 °C, 46:34:20 mixture of regioisomers) δ 7.48–7.34 (m, 2H, HAr), 7.25–6.78 (m, 22H, HAr), 1.22 (s, 1.84H, HtBu,regio3), 1.15 (s, 2.97H, HtBu,regio2), 1.11 (s, 4.04H, HtBu,regio1); 13C{1H} NMR (126 MHz, CD2Cl2, 25 °C, 46:34:20 mixture of regioisomers) δ 151.5 (Cquat–tBu), 150.8 (Cquat–tBu), 150.5 (Cquat–tBu), 148.4 (Cquat), 148.3 (Cquat), 147.9 (Cquat), 147.6 (Cquat), 143.4 (Cquat), 143.2 (Cquat), 143.1 (Cquat), 143.0 (Cquat), 136.8 (Cquat), 136.5 (Cquat), 135.5 (Cquat), 135.1 (Cquat), 135.0 (Cquat), 134.5 (Cquat), 134.3 (Cquat), 133.1 (Cquat), 131.8 (Cquat), 130.9 (Cquat), 130.6 (CPh–H), 130.5 (CPh–H), 130.3 (CPh–H), 130.2 (CPh–H), 129.9 (CPh–H), 129.8 (CPh–H), 128.9 (CPh–H), 128.3 (CPh–H), 128.1 (CPh–H), 128.0 (CPh–H), 127.8 (CPh–H), 127.6 (CPh–H), 127.5 (CPh–H), 126.7 (CPh–H), 126.6 (CPh–H), 126.4 (CPh–H), 125.8 (CPh–H), 125.0 (CPh–H), 124.8 (CPh–H), 82.4 (Cquat–Cl), 82.3 (Cquat–Cl), 82.2 (Cquat–Cl), 34.8 (CtBu), 34.7 (CtBu), 31.4 (CtBu), 31.3 (CtBu), 31.2 (CtBu).; HR-MS (spiral-TOF) signal: calcd for C39H33Cl [M]+: 536.2265, found. 536.2266.
2,3,4,5-Tetraphenyl-1-(pyrimidin-5′-yl)cyclopenta-2,4-dien-1-ol CpOHAr2 (100 mg, 0.22 mmol, 1 eq.) was placed in a round-bottom flask equipped with a magnetic stirring bar. Benzene (2.5 mL) was added and the suspension was heated to reflux using a preheated oil bath. Thionyl chloride (94 μL, 1.29 mmol, 6 eq.) was then added, and the mixture was refluxed for 30 minutes. The reaction medium was then cooled down, diluted with ethyl acetate (20 mL) and washed with a saturated aqueous solution of sodium hydrogen carbonate (20 mL) followed by distilled water (2 × 20 mL). The organic layer was then dried with magnesium sulfate and the solvents were evaporated to dryness. TLC of the crude (SiO2, ethyl acetate/hexane 3:7) showed only one spot resulting from a quantitative conversion of the starting material. The crude product was dissolved in ethyl acetate and filtered through a silica plug, using the same solvent for elution, to remove eventual impurities or salts. The solvent was then removed using rotary evaporation to give pure product CpClAr2 in 96% yield (99.3 mg, 0.21 mmol) as a pale-yellow solid composed of a 57:37:6 mixture of regioisomers.
Rf = 0.5 (SiO2, ethyl acetate:hexane 3:7); 1H NMR (500 MHz, CD2Cl2, 25 °C, 57:37:6 mixture of regioisomers): δ 9.06 (s, 0.06H, Haregio3), 8.91 (s, 0.57H, Haregio2), 8.85 (s, 0.37H, Haregio1), 8.80 (s, 0.12H, Hbregio3), 8.25 (s, 0.75H, Hbregio1), 8.23 (s, 1.15H, Hbregio2), 7.59–7.46 (m, 2H, HPh), 7.41–6.83 (m, 18H, HPh); 13C{1H} NMR (126 MHz, CD2Cl2, 25 °C, 57:37:6 mixture of regioisomers): δ 157.5 (Cpyr–H), 157.4 (Cpyr–H), 157.3 (Cpyr–H), 157.2 (Cpyr–H), 155.5 (Cquat), 152.3 (Cquat), 149.7 (Cquat), 148.7 (Cquat), 146.4 (Cquat), 143.0 (Cquat), 141.9 (Cquat), 136.3 (Cquat), 135.4 (Cquat), 135.3 (Cquat), 134.4 (Cquat), 134.3 (Cquat), 133.7 (Cquat), 133.6 (Cquat), 133.2 (Cquat), 130.7 (CPh–H), 130.6 (CPh–H), 130.4 (CPh–H), 130.3 (CPh–H), 130.1 (CPh–H), 129.4 (CPh–H), 129.1 (CPh–H), 129.0 (CPh–H), 128.9 (CPh–H), 128.8 (Cquat), 128.7 (CPh–H), 128.6 (CPh–H and Cquat), 128.5 (CPh–H), 128.4 (CPh–H), 128.3 (CPh–H), 126.7 (CPh–H), 126.5 (CPh–H), 82.1 (Cquat–Cl), 81.9 (Cquat–Cl); HRMS (DCI-CH4): calcd for C33H24N2Cl [MH]+: 483.1628, found 483.1642.
Rf = 0.8 (SiO2, dichloromethane/hexane 1:1); mp 93–95 °C; 1H NMR (600 MHz, (CD3)2CO, 25 °C): δ 7.59–7.58 (m, 2H, HPh), 7.36–7.25 (m, 3H, HPh), 7.11–7.01 (m, 11H, HPh), 6.97–6.93 (m, 4H, HPh), 6.81 (s, 1H, HMes), 6.79 (s, 1H, HMes), 2.20 (s, 6H, HMe), 2.15 (s, 3H, HMe); 13C{1H} NMR (151 MHz, (CD3)2CO, 25 °C) δ 148.7 (Cquat), 146.7 (Cquat), 143.1 (Cquat), 142.5 (Cquat), 137.2 (Cquat), 136.7 (Cquat), 136.1 (Cquat), 135.8 (Cquat), 134.6 (Cquat), 134.0 (Cquat), 133.7 (Cquat), 131.8 (Cquat), 130.3 (CPh–H), 129.3 (CPh–H), 128.7 (CPh–H), 128.4 (CMes–H), 128.3 (CMes–H), 128.3 (CPh–H), 128.0 (CPh–H), 127.7 (CPh–H), 127.6 (CPh–H), 127.5 (CPh–H), 127.4 (CPh–H), 127.3 (CPh–H), 126.4 (CPh–H), 81.8 (Cquat–Cl), 20.3 (CMe), 20.3 (CMe), 19.5 (CMe); HR-MS (MALDI): calcd for C38H31Cl [M]+: 522.2109, found 522.2106.
Rf = 0.2 (SiO2, dichloromethane/hexane 1:1); mp 206–208 °C (dec.); IR: νmax/cm−1 2037 (CO) and 1988 (CO); 1H NMR (600 MHz, CD2Cl2, 25 °C): δ 7.24–7.21 (m, 4H, HAr), 7.13–7.04 (m, 18H, HAr), 6.95 (d, 3J = 8.9 Hz, 2H, HAr), 1.24 (s, 9H, HtBu); 13C{1H} NMR (151 MHz, CD2Cl2, 25 °C): δ 197.4 (CO), 152.2 (Cquat–tBu), 132.8 (CAr), 132.8 (CAr), 132.4 (CAr), 130.3 (CAr), 130.2 (CAr), 128.7 (CAr), 128.1 (CAr), 125.1 (CAr), 107.6 (CCp), 107.3 (CCp), 106.6 (CCp), 34.9 (CtBu), 31.3 (CtBu); HR-MS (ESI+): calcd for C41H33BrNaO2Ru [M + Na]+: 763.0607, found. 763.0619.
Rf = 0.2 (SiO2, dichloromethane/hexane 1:1); mp 203–205 °C (dec.); IR: νmax/cm−1 2040 (CO) and 1989 (CO); 1H NMR (500 MHz, (CD3)2CO, 25 °C): δ 7.32–7.23 (m, 10H, HPh), 7.16–7.13 (m, 2H, HPh), 7.02–6.99 (m, 4H, HPh), 6.94–6.93 (m, 5H, HPh and HMes), 6.77 (s, 1H, HMes), 2.57 (s, 3H, HMe), 2.22 (s, 3H, HMe), 1.99 (s, 3H, HMe); 13C{1H} NMR (126 MHz, (CD3)2CO, 25 °C): δ 198.0 (CO), 138.9 (Cquat–Me), 138.0 (Cquat–Me), 137.2 (Cquat–Me), 132.6 (CAr), 131.2 (CAr), 130.5 (CAr), 129.6 (CAr), 129.0 (CAr), 128.6 (CAr), 128.5 (CAr), 128.2 (CAr), 127.7 (CAr), 127.2 (CAr), 113.9 (CCp), 103.2 (CCp), 22.9 (CMe), 21.1 (CMe), 20.1 (CMe); HR-MS (ESI+): calcd for C40H31BrNaO2Ru [M + Na]+: 747.0450, found 747.0451.
Rf = 0.2 (SiO2, dichloromethane/hexane 1:1); mp 197–199 °C (dec.); IR: νmax/cm−1 2038 (CO) and 1985 (CO); 1H NMR (600 MHz, CD2Cl2, 25 °C):δ 7.24–7.20 (m, 4H, HAr), 7.13–7.04 (m, 18H, HAr), 6.96–6.95 (m, 2H, HAr), 1.24 (s, 9H, HtBu); 13C{1H} NMR (126 MHz, CD2Cl2, 25 °C): δ = 197.8 (CO), 152.1 (Cquat–tBu), 132.7 (CAr), 132.6 (CAr), 132.2 (CAr), 130.3 (CAr), 130.2 (CAr), 128.7 (CAr), 128.2 (CAr), 128.1 (CAr), 125.1 (CAr), 107.8 (CCp), 107.4 (CCp), 106.6 (CCp), 34.9 (CtBu), 31.3 (CtBu); HR-MS (ESI+): calcd for C41H33ClNaO2Ru [MNa]+: 717.1110, found 717.1097.
Rf = 0.2 (SiO2, dichloromethane/hexane 1:1); mp 189–191 °C (dec.); IR: νmax/cm−1 2045 (CO) and 1996 (CO); 1H NMR (500 MHz, (CD3)2CO, 25 °C): δ 7.32–7.23 (m, 10H, HPh), 7.15 (t, 3J = 7.4 Hz, 2H, HPh), 7.03–6.99 (m, 4H, HPh), 6.94–6.92 (m, 5H, HPh and HMes), 6.77 (s, 1H, HMes), 2.57 (s, 3H, HMe), 2.21 (s, 3H, HMe), 1.99 (s, 3H, HMe); 13C{1H} NMR (126 MHz, (CD3)2CO, 25 °C): δ 198.0 (CO), 138.9 (Cquat–Me), 138.0 (Cquat–Me), 137.2 (Cquat–Me), 132.6 (CAr), 131.2 (CAr), 130.5 (CAr), 129.6 (CAr), 129.6 (CAr), 129.0 (CAr), 128.6 (CAr), 128.5 (CAr), 128.2 (CAr), 127.2 (CAr), 113.9 (CCp), 103.2 (CCp), 22.9 (CMe), 21.1 (CMe), 20.1 (CMe); HR-MS (ESI+): calcd for C40H31ClNaO2Ru [MNa]+: 703.0954, found 703.0976.
Footnote |
† Electronic supplementary information (ESI) available: HR-MS, IR, 1H and 13C-NMR spectra. See DOI: 10.1039/d1ra03875c |
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